Method for recycling vinyl polymer-based articles

ABSTRACT

Process for recycling an article based on at least one vinyl chloride or vinylidene chloride polymer, according to which:
     (a) the article is cut up into fragments with a mean size of 1 cm to 50 cm in the case where it would exceed these sizes;   (b) the article fragments are brought into contact with an azeotropic or quasiazeotropic mixture of water and of a solvent capable of dissolving the polymer, at a temperature of at least 120° C.;   (c) the polymer dissolved in the solvent is precipitated by a reduction in pressure and by injection of steam into the solution thus obtained, which additionally results in the entrainment of the solvent-water azeotrope and thus leaves a mixture remaining which is essentially composed of water and of solid polymer particles;   (d) the polymer particles are collected.

This application is a 371 of PCT/EP00/09150 filed Sep. 18, 2000, andclaims priority to French patent application 99/12036 filed Sep. 24,1999.

The present invention relates to a process for the recycling of articlesbased on vinyl polymers, such as vinyl chloride and vinylidene chloridepolymers.

These polymers are widely used in the manufacture of varied flexible orrigid articles, such as, for example, tarpaulins, coated fabrics andother components for the interior trim of vehicles, pipes, window framesor electrical cables possessing polymeric insulation.

Intensive grinding of these articles would generally result in a mixtureof fine particles with a heterogeneous composition, the purification andthe reuse of which would be difficult. In addition, in the case ofarticles reinforced with fibres (for example polyester fibres), thefibres often form a kind of wadding which greatly complicates the reuseof the ground materials.

Various processes based on dissolution by means of organic solvents havealready been provided; however, they often present problems of safetyand of pollution. In addition, they do not always make it possible tocollect plastics with a sufficient purity to make possible aneconomically advantageous reuse thereof. Another disadvantage of thesemethods is that they generally result in an extraction of the additives(e.g. plasticizers) present in the vinyl polymers, which goes against adirect reuse of the latter. Finally, these known processes result invery fine polymer particles (of the order of a micron) being obtained,which particles are difficult to filter and to reprocess.

Consequently, the present invention is targeted at providing a recyclingprocess which is simple, economic, safe and not very polluting and whichmakes it possible to collect plastics with a high purity andadvantageous morphology while substantially preventing the possibleadditives being extracted therefrom.

More specifically, the present invention relates to a process forrecycling an article based on at least one vinyl chloride or vinylidenechloride polymer, according to which:

-   (a) the article is cut up into fragments with a mean size of 1 cm to    50 cm in the case where it would exceed these sizes;-   (b) the article fragments are brought into contact with an    azeotropic or quasiazeotropic mixture of water and of a solvent    capable of dissolving the polymer, at a temperature of at least 120°    C.;-   (c) the polymer dissolved in the solvent is precipitated by a    reduction in pressure and by injection of steam into the solution    thus obtained, which additionally results in the entrainment of the    solvent-water azeotrope and thus leaves a mixture remaining which is    essentially composed of water and of solid polymer particles;-   (d) the polymer particles are collected.

The articles in question can be of any nature, provided that they areessentially composed of one or more vinyl chloride or vinylidenechloride polymers (“VC polymers”). The term “VC polymer” is understoodto denote any homo- or copolymer comprising at least 50% by weight ofvinyl chloride and/or of vinylidene chloride. Use is generally made ofpoly(vinyl chloride) (PVC) or poly(vinylidene chloride) (PVDC), that isto say a homopolymer. In addition to one or more VC polymers, thearticles can also comprise one or more conventional additives, such as,for example, plasticizers, stabilizers, antioxidants, flame-retardantagents, pigments, fillers, and the like, including reinforcing fibres,for example glass fibres or fibres of an appropriate plastic, such as apolyester.

The articles can be provided in any form, for example in the form offlexible or rigid pipes, containers, sheets for covering floors,tarpaulins, window frames, insulating sheaths for electrical cables, andthe like. They may have been manufactured by any known technique:extrusion, coating, injection moulding and the like.

The articles do not necessarily have to be provided in the form ofobjects exhibiting a well defined shape; the process also applies toarticles in the liquid or pasty state, in particular to sludgescollected during the cleaning of plants used for the manufacture ofarticles from vinyl plastisols. In addition to one or more vinylchloride polymers, these articles in the liquid or pasty state can alsocomprise one or more solvents, for example white spirit.

The possible reinforcing fibres can be of any nature, natural orsynthetic; use may in particular be made of glass fibres, cellulosefibres or plastic fibres. They are often plastic fibres and inparticular polyester fibres. Poly(ethylene terephthalate) (PET) givesgood results, in particular in the reinforcing of sheets used astarpaulins. The diameter of the fibres is usually of the order of 10 to100 μm. In the reinforced sheets, they are often long fibres, the lengthof which can reach several meters. However, they can also be shorterfibres, from a few millimeters to a few centimeters in length,optionally forming a woven fabric, a nonwoven fabric or a felt. By wayof illustration, the fibres can represent from 1 to 40% of the weight ofa reinforced sheet.

The first stage (a) of the process according to the invention consists,if necessary, in cutting up the articles so as to reduce them tofragments with a reduced size which are easy to handle. The mean size ofthese fragments is preferably at least 2 cm. Furthermore, it isadvantageously at most 30 cm. This operation in which the articles arecut up can be carried out by means of any appropriate device, forexample by means of grinders with rotating blades or with shears. It isclear that, if the article is already provided in the form of fragmentswith appropriate sizes, the stage in which the article is cut up issuperfluous. In some cases, it may be of use to subject the articlefragments thus obtained to an intermediate separation stage which makesit possible to remove by conventional techniques, such as flotation orelectrostatic separation, possible constituents other than vinylchloride or vinylidene chloride polymers.

The article fragments thus obtained are subsequently subjected to theaction of a solvent exhibiting several specific characteristics. Thisoperation can be carried out in any appropriate device, taking intoaccount in particular the safety and environmental requirements, forexample in a closed reactor exhibiting sufficient chemical resistance.The reaction mixture is preferably stirred. For the purpose ofpreventing the possible fibres from attaching to the stirring means andfrom disrupting their operation, an advantageous alternative formconsists in carrying out the dissolution in a container in which ispositioned a perforated rotary drum rotating at a moderate speed(preferably at less than 100 rev/min). The axis of the drum ispreferably approximately horizontal. In the case where the article isreinforced with fibres, an additional advantage of such a device isthat, after having extracted most of the solvent from this container, itis possible to rotate the drum at high speed, so as to “spin dry” thefibres which it comprises. The container(s) in which the dissolution andthe precipitation are carried out will be described as reactor(s) below.

The solvent used is a substance—or a mixture of substances—capable ofdissolving the vinyl chloride or vinylidene chloride polymer or polymerswhich the treated article comprises. However, in the case where thearticle is reinforced with fibres, the solvent must not bring about thedissolution of the reinforcing fibres. Surprisingly, it has been foundthat it is not essential to restrict the content of water in the solventto very low values, provided that a sufficient dissolution temperatureis used. It is therefore unnecessary to subject the articles to betreated to intensive drying or to provide stages targeted at greatlyreducing the content of water in the solvent. For example, if methylethyl ketone (MEK) is used as solvent, a temperature of 1050 correspondsto an MEK-water azeotrope comprising 15% of water, which constitutes ahigh content. The disappearance of these constraints is extremelyadvantageous industrially and economically, given that the drying of thearticles can consume considerable energy and that the separation of thewater present in the solvent (e.g. in methyl ethyl ketone (MEK)) is acomplex operation which requires at least one additional reactor, indeedeven a distillation column.

It is necessary, in the context of the process according to theinvention, for the solvent used to be miscible with water and to form anazeotrope with water. The solvent is advantageously chosen from methylethyl ketone (MEK), methyl isobutyl ketone and tetrahydrofuran. It ispreferable to use MEK, which forms an azeotrope with water comprising(at atmospheric pressure) 11% of water and 89% of MEK (by weight).

The fact that an azeotropic or quasiazeotropic mixture of water and ofsolvent is used for the dissolution constitutes, as will be seen below,a considerable simplification, in so far as such a mixture can easily berecovered at the end of the process (for example by a simple separationby settling) and can thus be directly reused. The expression “azeotropicor quasiazeotropic mixture” is understood to indicate that thecomposition of the mixture is not necessarily precisely equal to thecomposition of the azeotrope but that a slight deviation (e.g. of lessthan 5%) is acceptable, so as to take into account, in particular, thevariations in the azeotropic composition as a function of the pressure.This is because, as will be set out below, the final stages of theprocess are carried out at a pressure lower than that prevailing duringthe dissolution; this implies that the content of water in thewater-solvent (azeotropic) mixture collected at the end of the processis somewhat lower than the content of water in the water-solventazeotrope at the dissolution pressure.

The dissolution (stage b) is carried out under a pressure determined bythe temperature. This pressure is generally at least 4 bar. The pressureadvantageously does not exceed 10 bar.

In addition, it is advantageous to operate under an inert atmosphere,for example under nitrogen, in order to avoid any risk of explosion andof decomposition of the solvent.

The amount of solvent to be used must be chosen so as to prevent theincrease in viscosity brought about by the dissolution of the polymerfrom disrupting the satisfactory progression of the process (filtration,and the like). It is preferable, during the dissolution stage (b), forthe amount of article not to exceed 200 g per liter of solvent and inparticular 100 g/l.

From the viewpoint of a reuse of the VC polymer thus collected, anadvantageous alternative form of the process according to the inventionconsists in incorporating in the solvent, before or during the stage ofdissolution of the polymer, one or more additives (stabilizers,plasticizers, and the like), the natures and the amounts of which aresuited to the properties which it is desired to confer on the recycledpolymer. It is desirable, in this case, for the additive or additivesthus incorporated to be soluble in the solvent used. However, possibleinsoluble additives can be finely dispersed in the solvent.

On conclusion of the dissolution stage (b), there is available a mixturecomprising, on the one hand, a liquid phase composed of the solvent inwhich the polymer is dissolved and, on the other hand, the possibleundissolved constituents, for example reinforcing fibres. The separationof such constituents can be carried out, for example, by filtrationusing a cloth or screen, the openings of which exhibit sizes of theorder of 0.1 to 10 mm. This separation must be carried out at atemperature which is sufficiently high to prevent any prematureprecipitation of the polymer; to this end, the temperature of themixture is advantageously maintained at at least 75° C. during thisseparation.

In the cases where the article is reinforced with fibres, it is foundthat the fibres thus recovered are high in purity. In order to increasethis purity, the fibres can optionally be subjected to a subsequentstage of centrifuging and/or of washing, for example using the samesolvent, for the purpose of removing possible residual traces ofpolymer. The solvent which would have been used for this washingoperation can advantageously be mixed with the fresh solvent used in thedissolution stage; the fact that it comprises traces of dissolvedpolymer is not detrimental to the effectiveness of the dissolution. Thefibres can be reused directly in the manufacture of plastic-basedreinforced articles.

In addition to possible fibres, this optional separation stage alsomakes it possible to collect possible “accessories”, such as metaleyelets, labels, and the like, incorporated in the article and whichwould not have been removed therefrom before it was subjected to theprocess according to the invention. Likewise, possible pieces of metalconductors which would have remained in electrical cable sheaths canalso be removed. If necessary, the solvent comprising the dissolvedpolymer can be filtered more finely for the purpose of removingtherefrom possible dusts or other insoluble particles, for example byusing a cloth or screen, the openings of which exhibit sizes of lessthan 200 μm, preferably less than 20 μn. As indicated above, thisseparation must also be carried out at a temperature which issufficiently high to prevent any premature precipitation of the polymer.

Consequently, the present invention relates in particular to a processas described above in which, before precipitating the dissolved polymer,the possible undissolved constituents are removed at a temperaturesufficient to prevent the precipitation of the polymer.

After having optionally separated the solid constituents, the dissolvedpolymer is precipitated (stage c) by reducing the pressure, whichgenerally results in a decrease in the temperature. The reduction inpressure is carried out down to a pressure to which a temperaturecorresponds which is sufficiently low for the polymer to begin toprecipitate, preferably down to atmospheric pressure. Furthermore, steamis injected, into the solvent comprising the dissolved polymer, in anamount sufficient to completely precipitate the dissolved polymer. Alarge excess of water (steam or liquid) with respect to the azeotropiccomposition is preferably added. For example, in the case of MEK, from 1to 3 kg of water per kg of MEK are generally added. The reduction inpressure and the injection of steam precipitate the VC polymer in theform of solid particles (still substantially devoid of additives at thisstage), the mean sizes of which are of the order of a micron.

Another effect of the injection of steam is to bring about theevaporation and the entrainment of the water-solvent azeotrope in thegaseous form out of the reactor comprising the solution. This azeotropecan subsequently be collected and condensed. The mixture which remains(which has not been evaporated) is essentially composed of water and ofsolid polymer particles. As long as the solution still comprisessolvent, the temperature of the gas phase lying above the solutionremains approximately equal to the boiling temperature of the azeotropeat the pressure used (by way of example, the evaporation temperature ofthe MEK-water azeotrope is approximately 73.5° C. at atmosphericpressure).

Advantageously, the precipitation of the polymer (stage c) is carriedout by the joint injection of steam and of liquid water, whichaccelerates the precipitation of the polymer. It is not injurious forthis water optionally to comprise a low concentration of solvent; thisis advantageous in so far as, as set out below, a subsequent stage ofthe process specifically provides water with a slight charge of solvent,which can thus be reused without specific purification.

As soon as the concentration of solvent in the solution becomessufficiently low, the additives dissolved in the solution deposit on thepolymer particles, which; in a highly advantageous way promotes theiragglomeration into grains (agglomerates) of the order of 500 μm, whichwill be very easy to filter, to handle and to reemploy subsequently (incontrast to particles of the order of a micron). Surprisingly, it hasbeen found that these polymer grains (agglomerates) exhibit a highlysatisfactory morphology and in particular a particle size which exhibitsvery little dispersion.

When virtually all the solvent has been entrained, the temperature ofthe gas phase—just like that of the liquid phase—approaches the boilingtemperature of water (at the pressure used during the precipitation),which constitutes an easy means of detecting the virtually completeremoval of the solvent.

Once the solution is substantially devoid of solvent, it is, however,advantageous to maintain a high temperature (for example by continuingthe injection of steam) for at least a further 5 minutes and preferablyfor at least 10 minutes, which surprisingly has a highly favourableinfluence on the properties and the morphology of the polymer particles(agglomerates) (hardness, particle size, bulk density, porosity, and thelike).

A very significant advantage of the removal of the solvent by means ofsteam is that most of the possible additives present in the treatedpolymer are not entrained with the solvent and are redeposited on thepolymer particles. Consequently, the polymer particles collected onconclusion of the process still comprise a significant fraction of theadditives which were initially present in the polymer (at least those ofthese additives which are soluble in the solvent; this generally doesnot affect the possible fillers, for example). This situation isparticularly advantageous given that these additives are often expensiveand that, in addition, the said particles can thus be reused directly ina process for the manufacture of articles based on this polymer. Thisreuse is facilitated by the fact that the particles thus recovered arepregelled, which simplifies the processing in comparison with theprocessing of a heterogeneous mixture of polymer granules and ofadditives added separately. Known processes for recycling bydissolution-precipitation do not exhibit this advantage, in view of thefact that they result in the extraction of the majority of the additivesfrom the polymer.

An additional advantage of the injection of steam is that it generallyrenders superfluous external heating of the reactor in which the processtakes place. This advantage is very important industrially: this isbecause external heating (via the wall of the reactor) would result inpolymer encrustations on the wall of the said reactor (caking),requiring it to be frequently cleaned. In contrast, in the process ofthe invention, the injection of steam allows the wall to be at a lowertemperature, which greatly reduces the risks of caking.

Another advantage of the process of the invention is that the possibleemulsifiers which were present in the treated polymer pass into solutionin the water and that the polymer particles collected on conclusion ofthe recycling are consequently substantially devoid of emulsifiers,which facilitates the use thereof; in particular, deposits on theprocessing plants are avoided, as well as the formation of bubbles atthe surface of the novel products thus obtained.

The polymer particles (agglomerates) can then be easily collected (staged), for example by filtration of the water-particles mixture, andoptionally dried before being stored or reused. The residual water isadvantageously purified in order to remove the dissolved constituentstherefrom, such as emulsifiers or others.

Given the cost of the solvent and the disadvantages which its dischargeinto the environment might exhibit, it is desirable to recycle thesolvent/water liquid fraction (richer in water than the azeotrope)collected on conclusion of the precipitation stage. A significantadvantage of the process of the invention is that it is possible torecycle the liquid fraction in a very simple way and to completely reuseit. This is because a simple separation by settling makes it possible toseparate the liquid fraction collected into:

-   -   on the one hand, an (upper) fraction with a (quasi)-azeotropic        composition, that is to say predominantly of solvent, comprising        approximately 10% of water (the exact content of water depends        on the temperature and on the pressure), which can be reused in        the dissolution stage;    -   on the other hand, a (lower) fraction predominantly of water        (comprising, e.g., of the order of 80% of water), which can be        reused in the form of liquid water and/or of steam (after        reheating) in the precipitation stage (surprisingly and        advantageously, the presence of a small proportion of solvent is        not detrimental).

Despite these operations in which water is recycled, an additionalcontribution of water is generally necessary.

The process according to the invention can be carried out continuouslyor batchwise, the latter alternative form being preferred.

A major advantage of the said process is that it can operate in a closedloop, without polluting discharges being generated, given that both thesolvent and the possible agent for separating the solvent-water mixturecan be recycled and reused in the process.

DESCRIPTION OF THE FIGURE

The appended FIGURE diagrammatically illustrates in a non-limiting way,the progression of a specific alternative form of the process accordingto the invention, applied to the recycling of waste electrical cablesinsulated by a plasticized PVC sheath.

The symbols used have the following meanings:

P: solid polymer S: solvent (p): dissolved polymer W: water A:solvent/water azeotrope F: possible insoluble constituents STEAM: steam(which can comprise a small proportion of solvent).

The waste is first of all cut up (CUT) (stage a) and then the polymerwhich it comprises is dissolved (DISS) (stage b) under the effect of thesolvent/water azeotropic mixture (A), in which may optionally have beendissolved certain additives which it is desired to incorporate in thepolymer. The mixture thus obtained is then filtered (FILT1), which makesit possible to separate the possible insoluble constituents (F) (metalresidues, and the like) from a solution of the polymer in the solvent(S+(p)). The polymer is then precipitated (PREC) (stage c) by injectingsteam (STEAM) and optionally liquid water (“W(+S)”) (which can comprisea small proportion of solvent) into the solution, which also results inthe removal of the solvent-water azeotrope by entrainment. The solidpolymer particles P (agglomerates) are separated by filtration (FILT2)(stage d) from the water W, which is advantageously purified beforebeing discharged or reused, and then the particles are dried (DRY). Thefraction W+S collected during the separation, which is richer in waterthan the azeotrope, is condensed (stage not shown) and then separated bysettling (SETT), which provides on the one hand, a solvent/waterazeotropic fraction (A), which can be reused in the dissolution stage,and, on the other hand, a fraction predominantly of water (“W(+S)”),which can, for example, be reused in the precipitation stage, in theform of steam (STEAM) after a heating stage (H), as well as optionallydirectly in the liquid form.

1. A process for recycling an article comprising at least one of vinylchloride polymer and vinylidene chloride polymer, according to which:(a) the article is cut up into fragments with a mean size of 1 cm to 50cm in the case where it exceeds these sizes; (b) the fragments arebrought into contact with an azeotropic or quasiazeotropic mixture ofwater and of a solvent capable of dissolving the polymer, at atemperature of at least 120° C. to dissolve the polymer in the solvent;(c) the polymer dissolved in the solvent is precipitated by a reductionin pressure and by injection of steam into the solution of polymerdissolved in the solvent, which additionally results in the entrainmentof the solvent-water azeotrope and leaves a mixture remaining which isessentially composed of water and of solid polymer particles; (d) thepolymer particles are collected.
 2. The process according to claim 1,wherein stage (b) is carried out in a container in which is positioned aperforated rotary drum.
 3. The process according to claim 1, wherein thesolvent is chosen from the group consisting of methyl ethyl ketone(MEK), methyl isobutyl ketone, tetrahydrofuran and mixtures thereof. 4.The process according to claim 1, wherein stage (b) is carried out undera pressure of 4 to 10 bar.
 5. The process according to claim 1, whereinduring stage (b), the amount of article does not exceed 200 g per literof solvent.
 6. The process according to claim 1, wherein beforeprecipitating the dissolved polymer, undissolved constituents areremoved at a temperature sufficient to prevent the precipitation of thepolymer.
 7. The process according to claim 1, wherein the precipitationof the polymer in stage (c) is carried out by the joint injection ofsteam and of liquid water.
 8. The process according to claim 1, whereina solvent/water liquid fraction collected after conclusion of theprecipitation in stage (c) is separated by settling into: a firstfraction with an azeotropic or quasiazeotropic composition, which isreused in stage (b); a second fraction predominantly of water, which isreused in stage (c).
 9. The process according to claim 1, wherein thearticle is a sheet.
 10. The process according to claim 1, wherein saidarticle comprises vinyl chloride polymer.
 11. The process according toclaim 2, wherein said article comprises vinyl chloride polymer.
 12. Theprocess according to claim 3, wherein said article comprises vinylchloride polymer.
 13. The process according to claim 4, wherein saidarticle comprises vinyl chloride polymer.
 14. The process according toclaim 5, wherein said article comprises vinyl chloride polymer.
 15. Theprocess according to claim 7, wherein said article comprises vinylchloride polymer.
 16. The process according to claim 1, wherein saidarticle comprises vinylidene chloride polymer.
 17. The process accordingto claim 2, wherein said article comprises vinylidene chloride polymer.18. The process according to claim 3, wherein said article comprisesvinylidene chloride polymer.
 19. The process according to claim 4,wherein said article comprises vinylidene chloride polymer.
 20. Theprocess according to claim 5, wherein said article comprises vinylidenechloride polymer.
 21. The process according to claim 7, wherein saidarticle comprises vinylidene chloride polymer.